WO1996032053A1 - Method and device for measuring the level of secondary radiation produced by primary radiation incident on a zone of an object - Google Patents

Abstract

In order to measure the level of secondary radiation (4, 25) produced by primary radiation focussed on a zone (5) within an object (3), the invention calls for the primary and secondary radiation coming from or going to the zone (5) to be directed, in a common beam (17, 25), towards the same optical element (21) which focusses the primary radiation and collimates the secondary radiation into an optical fibre (30) leading to a measuring unit (29). In this beam, the primary and secondary radiation (i.e. the radiation transmitted into and retransmitted by the zone (5)) are conveyed parallel and cylindrically coaxial, but spatially separated from each other. Scattering and luminescence of light which can come only from the zone (5) within the object can be measured or otherwise determined. In addition, a relatively high light intensity can be produced at certain points within the object (3) being examined, the light intensity rapidly decreasing outside the object so that there is no danger of damage to the surrounding areas or the walls of the object (3). It is also possible to determine scatter and luminescence in the interior (1) of an object (3) which is only accessible to rays via an aperture (32), the position of the scatter and luminescence zone (5) being definable to such a degree of certainty that it can be kept away from radiation-sensitive zones.

Description

erzeugten StrahlungMethod and device for measuring a second, of

generated radiation

The invention relates to a method according to the preamble of claim 1, a device according to the preamble of claim 4 and a use according to claim 9.

An "optical scattering analyzer" is known from US Pat. No. 5,072,731, in which a first radiation was focused into the eye at an angle to the optical axis. The radiation was supplied with a light guide from a radiation source. The second radiation generated at the focal point in or on the eye was collimated with a lens arranged in the optical axis of the eye, deflected, then coupled into a further light guide and guided to a detector.

An optical measuring device is known from US Pat. No. 4,253,744, in which the radiation from a radiation source is applied a small diverter was focused and redirected. This deflected radiation was then focused with a focusing lens on the surface of the crown of the human eye and broadened again conically in the interior of the eye to illuminate the fundus. The radiation reflected from the back of the eye was collimated through the eye lens, focused by the focusing lens onto a focal point in front of the beam deflector in such a way that at least some of this reflected radiation radiated past the outside of the beam deflector, which then focused on a detector for measurement with a further focusing lens was focused.

An analog device is described in US Pat. No. 5,116,116, in which case the reflected radiation from the fundus is no longer guided past the edge of the U-mirror, but through a passage opening in the center thereof. The illuminating radiation is deflected in the edge area of the Ural steering mirror.

The object of the invention is to measure a method and a device for the optical measurement of a second radiation (scattered or linear radiation generated by a first radiation in a spatial area of an object, the spatial area being limited only by a spatially very limited one) View cross section is accessible.

The invention additionally solves the problem of creating a high intensity of the first radiation at the measuring location within the object to be measured, which intensity then rapidly decreases outside, so that surrounding areas or walls of the object are not exposed to any risk of damage from the first radiation.

The additional object of determining scatter and luminescence in the interior of an object is also achieved, which radiation can only be accessed via a covering opening, the position of the spatial region emitting the second radiation being reliably determinable in order to keep it from being radiated - to be able to keep away from sensitive areas or to choose a structure which allows measurement with a radiation intensity below the damage threshold.

The object is achieved in that the stimulating or illuminating (first) radiation and the reflected, scattered or (second) radiation emitted by optical excitation are shaped as parallel, cylindrical coaxial beams, whereby however, the two radiations are separate. This type of shaping of two beams allows them to pass through a spatially restrictive cross-section of the incoming and outgoing radiation separately from one another into the otherwise closed interior of a room. Appropriate adaptation of the passage cross sections or the radiations results in an almost complete use of the entire view cross section in terms of area. As a rule, a circular disc-shaped beam cross-section of a beam is used in the case of a circular see-through cross section which is surrounded by the other in a ring shape. If the cross-section of the view has a contour which deviates from this (for example square), one becomes a corresponding beam cross _. Select cuts (e.g. a square in a square ring). Due to the good use of area, an optimal intensity setting of the illuminating beam is also possible, such that, for example, no material changes can occur. It is also possible to work with high sensitivity with a view to the second beam. Only the fundamental optical laws of light propagation such as diffraction effects, diffraction limitation etc. form a limitation.

In a preferred manner, the beam generating the scatter is now designed as a “hollow beam”, into whose “cavity” the scattered radiation is then returned. Due to the preferred configuration of the exciting beam as a hollow beam, it results after the focusing lens outside the focal point on a catcher a ring, from the diameter of which the distance of the focus point from the catcher can be specified given a known focus length.

By "nesting" the first beam generating the second radiation with the generated second radiation, optimal beam guidance into the interior of an object is also possible through an opening covering it. The beam cross section of the outer (first) beam is selected so large in connection with the focusing element that it can just be guided through the opening after this in order to achieve the greatest possible focusing. Is z. For example, if the vitreous of the human eye is measured, the beam cross-section is selected such that it is not delimited by the edges of the eye lens at a focal point directly above the retina. Since one beam now focuses and the other is collimated by one and the same element, it is also possible to clearly assign the location measured or to be measured. For this purpose, the radiation detector is used against a second one

Radiation source replaced. Due to the "reversal of the radiation direction" it is now very easy to check whether the radiation emitted from the specified location (focal point) would also come into the detector. This is always the case as soon as the radiation of the first and the second radiation unite in one point. To simplify the adjustment, light of different colors, in particular laser radiation, can be used. A focus point shift owing to the different wavelengths can be neglected in the first approximation.

The incoming radiation and the scattered radiation are preferably supplied via light guides to which the radiation detector and the radiation source can be coupled. If the two light guides are designed as single-mode light guides for the basic mode, the first radiation can be focused well into a very small focal point owing to its intensity distribution having a Gaussian cross section the second radiation can be detected selectively with a high transverse coherence, such as e.g. B. in J. RiCka, "Dynamic light scattering with single-mode and multimode receivers", Applied Optics, Vol. 32, No. 15, May 20, 1993, pp. 2860-2875. With the device described here, even with the high selectivity z. B. can be worked with an exciting beam with a power of only 10 μW. A device that manages with such low performance is ideal for measuring on the vitreous of the human eye. On the basis of an embodiment of the device according to the invention described below, it can be avoided that the sensitive retina could be hit by a radiation intensity damaging it.

The invention is by no means restricted to the human eye. This example should only illustrate the high sensitivity of the reflected, scattered or generated (second) radiation as well as the use of a relatively high intensity of the irradiating (first) radiation without endangering the eye or its retina in an easily visible representation .

Instead of the eye, any object (space) can be imagined that is only accessible through a very limited cross-section of the view. Just think of high-pressure windows in combustion chambers (flame spectroscopy, ...), in which combustion processes must be checked or determined optically in accordance with the above-mentioned explanations with a first and a second radiation. The device and the method described below can also be used in chemical systems which, for example, only allow small windows (for example diamond windows) for cost reasons.

An example of the device according to the invention and of the method according to the invention is explained in more detail below with the aid of a schematic illustration. Further advantages of the invention result from the following Descriptive text.

In the schematic illustration, for example, the light scattering property of the vitreous body 1 of the human eye 3 is measured, on the cornea 31 of which a contact glass 2 is placed. The first radiation 7 which generates the scattered radiation in a predetermined spatial region 5 in the eye 3 comes from a light source 9, e.g. B. a He-Ne laser or a diode laser. Starting from the light source 9, the radiation 7 is guided over a light guide 10 and, at the other end thereof, is converted with a collimator 11 into a collimated beam 12 with the diameter d. Arranged in the beam axis of the collimated beam 12 is an optical element 13 inclined at 45 °, the central surface 14 facing the collimator 11 is absorbent and the opposite surface 15 is mirrored. The diameter e of the optical element 13 projected perpendicular to the beam axis is chosen so large that only a central part of the collimated beam 12 is shadowed, as a result of which an annular, "hollow cylindrical"

Beam 17 is created. This beam 17 is deflected by 45 ° with a deflecting mirror 19 and then focused into the vitreous body 1 of the eye 3 with a focusing lens 21, the divergence of the focused beam being chosen to be as large as that due to the diameter of the eye lens 32 defined entry opening just allowed.

If a single-mode light guide has now been selected as the light guide 10, the radiation 7 has an intensity distribution which is Gaussian in cross section and can therefore be focused at the focus point 5 to a minimum diameter which is smaller the larger the beam diameter of the beam 12 and the smaller the focal length of the focusing lens 21 is.

After the focal point 5, the beam expands and a ring 23 can then be seen on the retina 22. From the diameter of the ring 23, the focal length of the focus sierlinse 21 is known to unambiguously infer the distance of the focal point 5 from the retina 22.

In all areas of the "hollow beam" 17, most strongly at its focal point 5, scattered radiation 4 is generated in accordance with the existing scattering centers. A special spatial scatter characteristic is not discussed here. A part 4 of this scattered radiation is formed by the focusing lens 21, which now acts as a collimator, into a collimated ("full") beam 25, which with the deflecting mirror 19 and through the reflecting surface 15 of the optical element 13 into a Coupling unit 27 for coupling this radiation 25 into a light guide 30 connected to a detector 29 is directed. A single-photon avalanche diode is preferably used as the detector 29. The arrangement of the focusing lens 21, the reflecting surface 15, the coupling unit 27 and the selection of the type of light guide used - a single-mode light guide is used here owing to the high selectivity required (in particular coherence selectivity) - is selected tive selection of the backscattered radiation. Only this beam path is shown in the illustration.

As can easily be seen from the illustration, only the scattered radiation of the beam path 25 from the volume of the focal point 5 can reach the light guide 30 and thus the detector 29. This results from the fact that the first beam overlaps only at the focal point 5. For example, radiation scattered by the cornea 31 or by the eye lens 32 would not get into the light guide 30 and thus would not be measured by the detector 29.

The scattered radiation can now also be selected by selecting the light guide 30 as a single-mode fiber. As a result, only a transversely coherent radiation mode is selected from the scattered radiation, so that due to the scattering characteristic in the Focus point 5, the radiation incident on the detector 29 has large temporal fluctuations. Based on these fluctuations, temporal fluctuations in the density in the examined location 5 can be concluded. So z. B. viscoelastic properties of the vitreous body of the human eye can be measured. The selective selection of a single radiation mode also enables a distinction to be made between radiation components which result from tissue fluctuations and which result from fixed tissue parts.

If only a high sensitivity is required, one works with multimode light guides. Due to the interchangeability of the light guides 10 and 30, the desired optimal light guide type can be used without any problems.

Furthermore, a polarizer 33 can be introduced into the collimated radiation 25.

So that only scattered radiation from the volume of the

Focus point 5 is evaluated, an exact adjustment of the collimator 11, the optical element 12, the deflecting mirror 19, the focusing lens 21 and the coupling unit 27 must be carried out. An umbrella (not shown) is now set up at the location of the retina 22. The optical elements 11, 13, 19 and 21 located in the illuminating beam path 7, 12 and 17 are now set such that the ring 23 appears on the screen. The detector 29 is replaced by a light source, not shown. The light from the new radiation source instead of the detector 29 now emerges via the coupling unit 27 as a collimated beam, is deflected by the reflecting surface 13 and the deflector 19 and is focused with the focusing lens 21. The decoupling unit 27 is pivoted and its lateral position relative to the reflecting surface 13 is adjusted until the radiation from the light source replacing the detector 29 lies in the center of the ring 23. Even if the distance of the focusing lens 21 changes, it must be remain in the central position. If the distance of the focal point from the screen changes, the diameter of the radiation ring 23 of the light source 9 and the diameter of the circular disk of the radiation emanating from the light source replacing the detector change.

Since the illuminating, first radiation is supplied from the light source 9 and the scattered radiation is returned to the detector 29 via a flexible light guide 10 or 30, the actual measuring apparatus, consisting of the optical elements 11, 13, 19, 21 and 27, compact and handy, separate from the i. a. voluminous light source 9 and evaluation unit - detector 29 with downstream evaluation electronics.

In order to measure the scattering properties of the vitreous body 1 of the eye 3, the distance of the adjusted lens 21 above the eye is now changed.

Instead of using an illuminating "hollow" beam with a scattering beam running centrally in it, the two beams can also be guided lying next to one another, the large divergence with optimal focusing of the exciting beam and the one described above being simple Determination of the position of the scattering location are no longer given.

It is possible to interchange the illuminating and the scattering beam path, but it must then be ensured that the focal point when measuring the vitreous body is not placed too close to the retina in order to avoid damage to it by the incident radiation.

Modulated stimulating radiation can be used to reduce the signal-to-noise ratio.

Instead of working with collimated rays, you can beams with one and the same divergence angle can also be used. These beams should also be arranged concentrically to one another. However, the use of collimated beams is advantageously carried out when using light guides.

The deflecting mirror 19 is not absolutely necessary. However, it is preferably designed in such a way that its central region 35, with which the second beam 25 is deflected, bears a 100% reflection for the wavelength of the second radiation. The area 37 surrounding the area 35 is partially transparent, so that the luminous ring 23 used for determining the distance on the retina 22 can be evaluated with an observation optical system 39.

In most measuring methods, the wavelength of the radiated radiation is equal to the scattered radiation. However, there can also be an optical excitation of the material in the focus, so that an additional radiation frequency is then generated. Through a suitable selection, in particular of the light guide 30 and a filter instead of the polarizer 33 or in addition to this, only this radiation can then be evaluated analogously to the above measurement method.

Instead of making the shading area 14 of the optical element 13 absorbent, it can also be made reflective. Part of this reflected first radiation can then be used in a second detector to check the radiation intensity of the first radiation 7. The remaining reflected first radiation is then collected in an absorber.

Claims

claims 1. Method for measuring a second one generated by a first one in a spatial area (5) of an object (3) Radiation, characterized in that the first and the second radiation (17, 25) are guided together as parallel, cylindrically coaxial, but separate rays of a bundle of rays which run parallel to one another and with one and the same optical element (21) the first radiation (17) is focused in the spatial area (5) and the second radiation (4, 25) emanating from the latter (5) is collimated in order to create optical material properties in a small spatial area lying in the depth of the object (5) to be measured through a spatially severely restricting view cross-section (32) with high sensitivity and high spatial resolution, which are only limited by the fundamental optical laws. 2. The method according to claim 1, characterized in that the first and second beams (17, 25) of the beam (17, 25) as a in a "hollow beam" _ (17) lying, preferably coaxial "full beam" (25) from which the second beam (25), in particular the "full beam", is blocked for transmission into an optical fiber (30). 3. The method according to claim 1 or 2, characterized in that only the basic mode of the second beam (25) is guided in the light guide (30), and local and temporal fluctuations in density in the spatial region (5) are determined from the intensity fluctuations of the transmitted transmitted basic mode radiation, and preferably the first radiation is supplied in an intensity distribution with a Gaussian basic mode . 4. Device for performing the method according to a of claims 1 to 3, characterized by one and the same first optical element (21) for focusing a first beam (12, 17) into a predetermined spatial area (5) lying in the depth of an object and for collimating a part of the area ( 5) generated second radiation (4) to form a second beam (25) and a second optical element (13) to form the first and second beams parallel, cylindrically coaxial, but separate from one another on the area (5 ) facing away from the first element (21), so small spatial areas (5) lying in the object depth through a highly spatially restricting viewing opening (32) between the first optical element (21) and the spatial area (5) can be measured with high sensitivity and high spatial resolution, which are only limited by the fundamental optical laws. 5. The device according to claim 4, characterized in that the second optical element (13) as a deflecting mirror (15) for the second beam (25) and simultaneous Shading element (14) for only a partial spatial shading of the first beam ( 12) is designed so that the second beam (25) can be guided in the area (s) that can be generated by the shading, and preferably the shading and deflecting second optical element (13) and the beam guidance of the first and second beams (17, 25) are arranged in such a way that both beams (17, 25) can thereby be guided coaxially and cylindrically together as a beam and in particular one of the beams is designed as a "hollow beam" (17), in the "cavity" ( e) the other beam (25) can be guided separately. 6. Apparatus according to claim 4 or 5, characterized by a light guide (30), which preferably acts as a spatial radiation filter for the radiation of the second beam (25) and is connected to a radiation measurement unit (29), which is in particular interchangeable and preferably in the form of a mono-light guide to increase the coherence selectivity while maintaining a maximum sensitivity of the measurement of the second radiation intensity, and by a further light guide (10) which is used to bring the first radiation from a radiation source ) is used, in particular also interchangeably and advantageously for minimizing the focus diameter of the first radiation to be focused, is designed as a single-mode light guide, and by a collimator (11) for collimating the radiation (12) emerging from the further light guide (10) to the first Beam (12, 17). 7. Device according to one of claims 4 to 6, preferably according to claim 7, characterized in that the radiation detector (29) of the one light guide (30) is designed to be interchangeable with a second radiation source, so that an opti due to a "radiation reversal" - Male coupling ability of the second radiation from the spatial area (5) into the one light guide (30) can be checked. 8. Device according to one of claims 4 to 7, characterized by an adjusting unit for the first optical element (21) acting in the axial direction of the coaxial first and second beams (17, 25) for shifting the spatial area (5 ) in the depth of the object as well as preferably an observation optics (39) and a partially partially transparent deflection mirror (19), with which the intensity of the first beam (17) can be partially deflected as well as that of the second beam (25), with the observation optics (39 ) can be observed through the partially permeable area (37) for determining the position of the room area (5). 9. Use of the device according to one of claims 4 to 8 for determining optical material properties, in particular the material scattering and luminescence with high sensitivity and high spatial resolution in a small spatial area, which can only be viewed through a spatial cross-section (32). 10. Use according to claim 9, characterized in that the viewing cross-section (32) opposite wall is sensitive to radiation and therefore may only be hit by a radiation density which is significantly smaller than that which is necessary for the determination of material scattering and luminescence and in particular on the human eye through the eye lens as a spatially restricting view opening in the vitreous body without ever having a radiation density which would endanger the retina.